The use of air bag systems in vehicles has increased significantly in recent years. In conjunction with the activation of the system whereby the bag is inflated, a header assembly commonly acts as an initiator in causing gases to fill the bag.
A known header assembly made by the assignee of the present invention includes an eyelet having a glass insulator and ceramic insert positioned through the center of the eyelet. The glass insulator is hermetically sealed in the eyelet. The ceramic insert has an outer surface that is substantially flush with an end of the eyelet. An epoxy is disposed in the eyelet bore before insertion of the ceramic insert. A center electrode pin is located co-axially relative to the glass insulator and ceramic insert. A side electrode pin is welded to the eyelet. A bridgewire is connected between an end of the center electrode pin and the eyelet with the wire extending over and contacting the ceramic insert. When power is applied, current flows between the center electrode pin and the eyelet, as well as the side electrode pin, through the conducting bridgewire. In operation with an air bag inflator system, the current through the bridgewire activates an ignitor component that ignites a propellant or generates gases for use in filling an air bag.
With respect to this prior art header assembly used in air bag systems, the ceramic insert is intended to provide a substantially smooth, flush surface so that there are no bubbles or cracks that may affect the bridgewire placed across the ceramic insert. That is, the outer surface of the eyelet together with the ends of the ceramic insert and center electrode pin, are made and assembled to be substantially even or flush with each other. In achieving the desired flushness, a grinding process is utilized. With respect to the use of the ceramic insert, both before and after the grinding process, it has been found to be free of bubbles or cracks that may act to degrade the bridgewire, which degradation may result in the bridgewire breaking. Although the ceramic insert achieves the desired result of a bubble or void-free outer end or surface, this header assembly does have the additional parts of a ceramic insert and epoxy, which are used with the glass insulator to insulate the center electrode pin.
In connection with military related applications, it is known to use initiator devices or header assemblies for ignition-related purposes. In these known uses, header assemblies have been provided in which the entire insulating body is made of a sealing glass. These known prior art devices have one or more features or characteristics that make them less appropriate for use in a vehicle air bag system. These attributes include eyelets that are not corrosion resistant, an uneven glass outer surface, and a less desirable glass composition.